The first discussions between Iran and six world powers on Tehran's nuclear programme have ended on a positive note, Western officials have said.

西方官员称，伊朗与六大世界强国之间关于德黑兰核计划的首轮会谈在有积极意义的消息中结束。

But some diplomats¹ said there was still a long way to go, and specific actions were needed from Iran.

The talks in Istanbul on Saturday were the first for 15 months. The next round will take place in Baghdad on 23 May.

Iran says its programme is peaceful, but critics suspect it of seeking to develop a nuclear weapons programme.

The European Union's foreign policy chief, Catherine Ashton, described the talks as "constructive² and useful".

Speaking at the end of the talks between the six countries - the US, UK, France, China, Russia and Germany - and Iran, Baroness³ Ashton said that future discussions would be guided by the "principle of a step-by-step approach and reciprocity（相互作用） ".

She said that Iran has the right to a peaceful nuclear programme, and that the nuclear Non-Proliferation Treaty must be a "key basis" for future talks.

The Iranian chief nuclear negotiator, Saeed Jalili, described Saturday's talks as being based on co-operation and "very successful".

He said next month's talks should focus on building mutual⁴ confidence.

Iran believes that it is entitled to enrich uranium up to 20% under the Non-Proliferation Treaty. Mr Jalili said that Tehran expects "that we should enjoy our rights in parallel with our obligations".

The British Foreign Secretary, William Hague, welcomed the talks, but said there was "a long way to go" to resolve the dispute.

The French Foreign Minister, Alain Juppe, said Iran needed "to make urgent and concrete gestures to establish confidence" in the next round of talks.

A White House spokesperson praised the "positive attitude" from Iran, describing Saturday's talks as a "first step".